Wall extensibility, wall pH and tissue osmolality: significance for auxin and ethylene-enhanced petiole growth in semi-aquatic plants

Abstract. Auxin and ethylene both enhance cell elongation in intact petioles of the semi-aquatic plants Regnellidium diphyllum and Nymphoides peltata. The authors now show that auxin but not ethylene increases the in vitro extensibility of cell walls. No response to ethylene occurs in auxin-depleted tissue. Neither hormone regulates cell expansion by direct control of internal osmolality (OS). During growth of segments, OS (and hence turgor) declines rapidly over the first 5–6 h with a net loss of osmotic solutes. Thereafter, an apparent threshold OS is maintained with net gains in osmostic solutes ( Nymphoides ) or further net losses ( Regnellidium ). Although wall extensibility determines initial rates of hormone-induced cell expansion, the primary control of wall loosening appears to differ in the two species. Nymphoides shows typical 'acid growth', and fusicoccin, auxin and ethylene (with auxin) all enhance proton secretion. In Regnellidium , neither low pH nor fusicoccin (FC) alters the rate of cell expansion, although proton secretion is stimulated by FC. Stress relaxation studies using low pH treatment of living or frozen-thawed segments show increases in the extensibility of walls in vitro for Nymphoides but not for Regnellidium. The authors propose that extensibility may be controlled by wall pH in Nymphoides but the availability of effective wall-loosening sites determines extensibility in Regnellidium.     

Physiological Properties of Abscission Accelerator from Senescent Leaves

A substance which is not abscisic acid accelerates leaf abscission by regulating ethylene production.     

Antibiotic Resistance among Escherichia coli O-serotypes from the Gut and Carcasses of Commercially Slaughtered Broiler Chickens: a Potential Public Health Hazard

Presumptive coliform counts and the distribution of Escherichia coli O-serotypes were investigated in chicken rectal contents (175) abdominal cavities (152) and on the carcasses of 44 which had been commercially raised, slaughtered and prepared for sale. Large numbers of E. coli resistant to at least one antibacterial agent were found at each site; comparison of the O-serotypes suggested heavy contamination of the carcass with strains from the gut. The range of O-serotypes was similar to that found in man and some public health implications of cross-infection particularly by handling uncooked birds in the kitchen, are discussed.     

The effect of tadpoles on algal growth in temporary, rain-filled rock pools

SUMMARY.

• 1 Small, temporary, rain-filled rock pools in Malawi, Central Africa, are colonized by algae, insect larvae and tadpoles. Algal growth in these pools is largely controlled by nutrient supply, flushing rate and the presence of tadpoles.
• 2 Dissolved nitrogen and phosphorus concentrations were usually high following filling but subsequently declined. Nitrogen supply may limit algal growth at times. The flushing rate of the pools is an over-riding factor in determining the population size of floating algae.
• 3 Experiments and field observations showed that tadpoles apparently, paradoxically, promoted the growth of the epineustic and phytoplanktonic algae on which they grazed. The explanation of this paradox probably has in the transfer, by the tadpoles, of nutrients from the sediments to the overlying water. This nutrient enrichment stimulates the growth of the epineuston and phytoplankton.

     

Cell Wall Metabolism in Developing Strawberry Fruits

Cell wall metabolism was studied in strawberry receptacles (Fragariaananassa, Duchesne) of known age in relation to petal fall (PF).Polysaccharide and protein composition, incorporation of [¹⁴C]glucoseand [¹⁴C]proline by excised tissue, and the fate of ¹⁴CO₂ fixedby young, attached fruits were followed in relation to celldivision, cell expansion, fine structure, and ethylene synthesis. Cell division continued for about 7 d after PF although vacuolationof cells was already beginning at PF and the subsequent cellexpansion was logarithmic. There was an associated logarithmicincrease in sugar content per cell and a decreasing rate ofethylene production per unit fresh weight. During cell expansion radioactivity from [¹⁴C]glucose was incorporatedinto fractions identified as starch and soluble polyuronideand into glucose and galactose residues in the cell wall. Radioactivityfrom [¹⁴C]proline was also incorporated into the cell wall,but only 10 per cent of this activity was found in hydroxyproline.Correspondingly wall protein contained a low proportion of hydroxyprolineresidues. The proportion of radioactivity from ¹⁴CO₂ fixed byfruitlets remained constant in most sugar residues in the cellwall. The proportion of radioactivity in galactose fell, indicatingturnover of these residues. Between 21 and 28 d after PF receptacles became red and softenedbut there was no change in the rate of ethylene production.Cell expansion continued for at least 28 d. Tubular proliferationof the tonoplast and hydration of middle lamella and wall matrixmaterial had begun 7–14 d after PF but became extremeduring ripening. Associated with the hydration of the wall,over 70 per cent of the polyuronide in the wall became freelysoluble, and arabinose and galactose residues lost from thewall appeared in soluble fractions. There was no increase intotal polysaccharide during ripening and incorporation of [¹⁴C]glucoseinto polysaccharides ceased, although protein increased andincorporation of [¹⁴C]proline into wall protein continued.     

Changes in the Distribution of Pectin Methylesterase across Leaf Abscission Zones of Phaseolus vulgaris

Determinations of pectin methylesterase in abscission zonesand surrounding parts of Phaseolus leaves have shown a relativelyhigh activity in young tissues, which decreases as the leafgrows older. The greatest fall occurs in the pulvinus. In non-senescent leaves, the enzyme activity is higher in pulvinithan elsewhere and there is a gradient of activity across theline of abscission from the pulvinus to the petiole or stem.During senescence this gradient falls, and is generally reversedat abscission. Data suggest that the advent of abscission maybe linked to the steepness of this gradient. If abscission of leaves or isolated abscission zones is acceleratedby appropriate treatments there is a more rapid decrease inpectin methylesterase activity than in the controls, and a morerapid fall in the gradient across the line of abscission. Ifabscission is retarded the enzyme activity is sustained andthe gradient is maintained or increased. The results are discussed in relation to the changes that mayoccur in the pectic constituents of cell walls during senescenceand abscission, and in relation to some of the known effectsof auxins on pectin metabolism.     

Biochemical and molecular characterisation of Tetrahymena thermophila extracellular cysteine proteases

Background  

Over the last decades molecular biologic techniques have been developed to alter the genome and proteome of Tetrahymena thermophila thereby providing the basis for recombinant protein expression including functional human enzymes. The biotechnological potential of Tetrahymena has been proved in numerous publications, demonstrating fast growth, high biomass, fermentation in ordinary bacterial/yeast equipment, up-scalability, existence of cheap and chemical defined media. For these reasons Tetrahymena offers promising opportunities for the development of a high expression system. Yet optimised high yield strains with protease deficiency such as commonly used in yeast and bacterial systems are not available.     

The bifunctional dihydrofolate reductase thymidylate synthase of Tetrahymena thermophila provides a tool for molecular and biotechnology applications

Background  

Dihydrofolate reductase (DHFR) and thymidylate synthase (TS) are crucial enzymes in DNA synthesis. In alveolata both enzymes are expressed as one bifunctional enzyme.     

Secretion of functional human enzymes by Tetrahymena thermophila

Background  

The non-pathogenic ciliate Tetrahymena thermophila is one of the best-characterized unicellular eucaryotes used in various research fields. Previous work has shown that this unicellular organism provides many biological features to become a high-quality expression system, like multiplying to high cell densities with short generation times in bioreactors. In addition, the expression of surface antigens from the malaria parasite Plasmodium falciparum and the ciliate Ichthyophthirius multifiliis suggests that T. thermophila might play an important role in vaccine development. However, the expression of functional mammalian or human enzymes remains so far to be seen.     

Estimation of bumblebee queen dispersal distances using sibship reconstruction method

Dispersal ability is a key determinant of the propensity of an organism to cope with habitat fragmentation and climate change. Here we quantify queen dispersal in two common bumblebee species in an arable landscape. Dispersal was measured by taking DNA samples from workers in the spring and summer, and from queens in the following spring, at 14 sites across a landscape. The queens captured in the spring must be full sisters of workers that were foraging in the previous year. A range of sibship reconstruction methods were compared using simulated data sets including or no genotyping errors. The program Colony gave the most accurate reconstruction and was used for our analysis of queen dispersal. Comparison of queen dispersion with worker foraging distances was used to take into account an expected low level of false identification of sister pairs which might otherwise lead to overestimates of dispersal. Our data show that Bombus pascuorum and B. lapidarius queens can disperse by at least 3 and 5 km, respectively. These estimates are consistent with inferences drawn from studies of population structuring in common and rare bumblebee species, and suggest that regular gene flow over several kilometres due to queen dispersal are likely to be sufficient to maintain genetic cohesion of ubiquitous species over large spatial scales whereas rare bumblebee species appear unable to regularly disperse over distances greater than 10 km. Our results have clear implications for conservation strategies for this important pollinator group, particularly when attempting to conserve fragmented populations.